1. Field of the Invention
The present invention relates to an in-vehicle communication system comprising a plurality of distribution apparatuses for distributing stored data and an onboard apparatus for receiving data distributed from the distribution apparatuses.
2. Description of Related Art
Recently, there are an increasing number of onboard instruments, as well as operation assistant functions, mounted on a car (motor vehicle). In proportion to the increasing numbers, a car tends to have an increasing number and an increasing number of types of ECUs (Electronic Control Units) that control electrically onboard instruments and operation assistant functions. Furthermore, in proportion to the increasing number of ECUs, data amounts are increased that are sent and received through a communication line within the car to which ECUs are connected.
It is common for such communication line within a car that ECUs are connected in a bus topology to a serial bus based on CAN (Controller Area Network) and the like. Thus, data is sent to all ECUs connected to the same communication line within the car, even when the data is utilized only by some ECUs. Therefore, data collision is caused by the increasing amounts of data sent and received in the communication line within the car, and then data delay or data deletion is caused by the data collision. A noticeable data delay or data deletion may happen to lead a critical defect for an operation assist function controlled by an ECU, such as a function for brake control.
Hence, it is common that a communication line within a car is branched into a plurality of communication lines and ECUs are connected to the communication lines suitably, because it is possible to minimize waste of usage about a communication line within a car by holding ECUs based on common data. In addition, it is known to categorize ECUs into groups based on types of sent and received data, and then to suitably connect the groups to communication lines within a car having different communication speeds, in order to utilize the communication lines efficiently in consideration of an increasing number of types of ECUs. In these configurations, a gateway apparatus is utilized to connect different communication lines within a car to each other, and the gateway apparatus controls to send and receive data. Thus, the gateway apparatus functions as a distribution apparatus that temporally stores data received from an ECU and distributes/sends the stored data to an onboard apparatus which requires the stored data.
A patent document 1 discloses a technique: to separate ECUs into a plurality of groups; connect ECUs to a communication line per the groups; further connect the communication line to a gateway apparatus; add priority information to received and sent data for identifying a priority level; determine a priority level based on priority information of received data, when the gateway apparatus sends or receives data between different communication lines within a car; and to preferentially send data having the highest priority level in order to prevent a noticeable delay in a transmission of data having a higher priority level. [Patent document 1] Japanese Patent Application Laid-Open No. 2005-159568